Abstract: This work focuses on the study of the generation and propagation of modes with orbital angular momentum in unguided and guided media (comprising specially-designed optical fibers and integrated waveguides), aiming at their application in mode-division multiplexing for optical communications. In the case of unguided media, we analyze the general properties of modes with orbital angular momentum and develop a novel study of the polarization properties of Frozen Waves, resulting in a technique to control the intensity and polarization patterns of diffraction-attenuation-resistant beams along their propagation. Regarding the specially-designed optical fibers, we start with the study of the composition of modes with orbital angular momentum in cylindrical fibers and the difficulties for propagating them robustly in conventional fibers. Then, we analyze the characteristics of the vortex fibers and how they diminish the coupling among modes, in particular the ones with orbital angular momentum. Finally, we propose a method to enhance the properties of these fibers by using anisotropic dielectric metamaterials in their claddings, providing results such as improved modal confinement, higher separation among effective indexes, increased number of supported modes and higher mode robustness when subject to perturbations, such as bends. In the case of integrated waveguides, we exploit the generation and propagation of modes with orbital angular momentum in rectangular waveguides, based on a proposal in the literature. Although it advocates the robustness of the proposed method, we notice that, in reality, there are many challenges in order to successfully propagate these modes in this kind of waveguide that were not previously addressed. Therefore, we carry a detailed and comparative analysis on the robustness of modes with orbital angular momentum with respect to the conventional modes of rectangular waveguides, taking into consideration different materials, fabrication imprecisions, bends and local or persistent perturbations. The results show that the conventional modes are more suitable for mode-division multiplexing (that is, they have smaller chances of coupling when subject to perturbations and are more easily excited), although modes with orbital angular momentum in integrated platforms may be useful for other important applications, such as optomechanics